5 Bizarre Paradoxes Of Time Travel Explained

A Predestination Paradox occurs when the actions of a person traveling back in time becomes part of past events, and may ultimately causes the event he is trying to prevent to take place.

Imagine that your lover dies in a hit-and-run car accident, and you travel back in time to save her from her fate, only to find that on your way to the accident you are the one who accidentally runs her over. Your attempt to change the past has therefore resulted in a predestination paradox.

Any attempts to stop something from happening in the past will simply lead to the cause itself.

A Bootstrap Paradox is a type of paradox in which an object, person, or piece of information sent back in time results in an infinite loop where the object has no discernible origin, and exists without ever being created.

A bootstrap paradox involving a person: a 20 year old male time traveler who goes back 21 years, meets a woman, has an affair, and returns home three months later without knowing the woman was pregnant. Her child grows up to be the 20 year old time traveler, who travels back 21 years through time, meets a woman, and so on.

For example, if you traveled to the past and killed your grandfather, you would never have been born and would not have been able to travel to the past – a paradox. 

Let’s say you did decide to kill your grandfather because he created a dynasty that ruined the world. You figure if you knock him off before he meets your grandmother then the whole family line (including you) will vanish and the world will be a better place.

Similar to the Grandfather Paradox which paradoxically prevents your birth, the Killing Hitler paradox erases your reason for going back in time to kill him.

Furthermore, while killing Grandpa might have a limited “butterfly effect”, killing Hitler would have wider consequences for everyone in the world, even just studying him in school.

The paradox itself arises from the idea that if you were successful, then there would be no reason to time travel in the first place. If you killed Hitler then none of his actions would trickle down through history and cause you to want to make the attempt.

American theoretical physicist Joseph Polchinski proposed a time paradox scenario in which a billiard ball enters a wormhole, and emerges out the other end in the past just in time to collide with its younger version and stop it going into the wormhole in the first place.

Solutions have been formulated to avoid the inconsistencies Polchinski suggested, essentially involving the billiard ball delivering a blow which changes its younger version’s course, but not enough to stop it entering the wormhole. This solution is related to the ‘timeline-protection hypothesis’

A self-fulfilling prophecy is only a causality loop when the prophecy is truly known to happen and events in the future cause effects in the past, otherwise the phenomenon is not so much a paradox as a case of cause and effect. 

Say, for instance, an authority figure states that something is inevitable, proper, and true, convincing everyone through persuasive style. People, completely convinced through rhetoric, begin to behave as if the prediction were already true, and consequently bring it about through their actions.

The Butterfly Effect is a reference to Chaos Theory where seemingly trivial changes can have huge cascade reactions over long periods of time. Consequently, the Timeline corruption hypothesis states that time paradoxes are an unavoidable consequence of time travel, and even insignificant changes may be enough to alter history completely.

In one story, a paleontologist, with the help of a time travel device, travels back to the Jurassic Period to get photographs of Stegosaurus, Brachiosaurus, Ceratosaurus, and Allosaurus amongst other dinosaurs.

He knows he can’t take samples so he just takes magnificent pictures from the fixed platform that is positioned precisely to not change anything about the environment. His assistant is about to pick a long blade of grass, but he stops him and explains how nothing must change because of their presence.

They finish what they are doing and return to the present, but everything is gone. They reappear in a wild world with no humans, and no signs that they ever existed. They fall to the floor of their platform, the only man-made thing in the whole world, and lament “Why? We didn’t change anything!”

And there on the heel of the scientist’s shoe is a crushed butterfly.

Scientists have suggested ingenious ways to avoid time travel paradoxes, including

–The Solution: time travel is impossible due to the very paradox it creates

–Self-healing hypothesis: successfully altering events in the past will set off another set of events which will cause the present to remain the same

–The Multiverse /“many-worlds” hypothesis: an alternate parallel universe or timeline is created each time an event is altered in the past

–Erased timeline hypothesis : a person traveling to the past would exist in the new timeline, but have their own timeline erased